The present invention relates to a metal gasket with different surface pressure portions or distinctive seal lines, which is useful for sealing a portion subjected to heat deformation and/or having low rigidity. The gasket is useful as a manifold gasket for connecting a cylinder head to a manifold, and a flange gasket for connecting a manifold to an exhaust pipe, or other device.
The manifold or exhaust pipe to which the manifold gasket or flange gasket is installed includes a flange at an end of a pipe. The rigidity of the flange is relatively low, and the flange is heated and cooled repeatedly because of high temperature exhaust gas passing through the manifold and exhaust pipe. Therefore, the flange expands and contracts, i.e. subjected to heat deformation, repeatedly whenever the engine is actuated.
The gasket for sealing the manifold or exhaust pipe must seal the flange which deforms according to heat. In particular, a surface configuration of the flange may be partly deformed, and a space to be sealed by the gasket may be changed, by the heat deformation of the flange. Since the gasket has to seal the deformed flange or flanges, the gasket must have sufficient compressibility or resiliency for absorbing the deformation of the flange.
Further, although the heat deformation at the flange occurs repeatedly when an engine is actuated, the resiliency of the gasket at the sealing portion must not be lost to securely seal at the flange. When a bead is used in the gasket for sealing the flange, it is required to prevent creep relaxation and crack formation at the bead.
In view of the requirements as stated above, a gasket 2 as shown in FIG. 4 has been proposed in Japanese Patent Publication (KOKAI) No. 4-219572. The gasket 2 is formed of a plate 22 with a bead 22b, and an upper plate 23 with a curved portion 23a and a flange 23b. The width Wb of the bead 22b is changed such that as the bead 22b approaches a bolt hole for the gasket 2, the width of the bead 22b is reduced and the height of the bead 22b is increased. In this gasket 2, when the gasket is tightened, the surface pressure formed on the bead becomes generally equal to thereby compensate the deformation of the flange.
In the gasket 2, a stopper portion 25 formed of three plate portions is established at the flange 23b, and the bead 22b extends from a portion above the flange 23b to a portion outside the flange 23b. Thus, when the gasket 2 is tightened, the bead 22b is not completely compressed by the stopper portion 25, which prevents creep relaxation of the bead 22b. However, since an area extending from the curved portion 23a to the bead 22b on the flange 23b is formed of the plate portions with the same thickness, a sealing portion for a hole 3 is formed of one portion extending from the curved portion 23a to the bead 22b.
Namely, in order to provide a sufficient sealing ability while absorbing a large heat deformation at the flange around the hole 3, a plurality of sealing areas must be formed around the hole 3. However, since the gasket 2 has one stopper portion 25 formed of the three plate portions, the thickness at the stopper portion 25 is the same. Thus, the surface pressure of the stopper portion 25 when the gasket 2 is tightened is gradually reduced, as shown in FIG. 5(b). Namely, an effective second sealing portion is not formed around the hole 3.
Also, since the gasket 2 has one bead 22b, a space to be sealed at the flange of the pipe is limited to the size of the bead 22b. Thus, if the space to be sealed is large, the bead 22b must be wide and high, which may result in creep relaxation of the bead. Further, since the height and width of the bead 22b are gradually changed, the manufacturing cost of the gasket is increased.
The present invention has been made in view of the above, and an object of the invention is to provide a metal gasket suitable for a gasket attaching portion with heat deformability and low rigidity.
Another object of the invention is to provide a metal gasket as stated above, which can provide a plurality of distinctive seal lines to securely seal around the hole.
A further object of the invention is to provide a metal gasket as stated above, which can provide large bead compressibility to securely seal around a hole.
A further object of the invention is to provide a metal gasket as stated above, wherein creep relaxation of the bead is reduced or avoided.
Further objects and advantages of the invention will be apparent from the following description of the invention.